1. Field of the Invention:
The present invention relates to a resistor having a high area resistance value usable in an image and video display device utilizing an electron source, for example, a cathode-ray tube (hereinafter, referred to as a xe2x80x9cCRTxe2x80x9d) or a field emission display (hereinafter, referred to as an xe2x80x9cFEDxe2x80x9d), a method for producing such a resistor, a cathode-ray tube including such a resistor, and an FED including such a resistor.
2. Description of the Related Art:
FIG. 6 is a schematic cross-sectional view of a conventional CRT 600 used in a color display apparatus. As shown in FIG. 6, the CRT 600 includes a face plate 601 acting as a fluorescent screen and a neck 602. The neck 602 accommodates a cathode 603 and an electronic lens system 607. The electronic lens system 607 includes a triode section 604 and a main electronic lens section 605 formed of a plurality of metal cylinders 605A and 605B. The electronic lens system 607 is structured so as to project a crossover image of an electronic beam from the cathode section 603 on the face plate 601 using the main electronic lens section 605. Reference numeral 606 represents a built-in division-type resistor.
In the electronic lens system 607 having such a structure, a diameter DS of a spot image on the face plate 601 is found by expression (1) using an electrooptic magnitude M and a spherical aberration coefficient CS0.
DS=[(Mxc3x97dx+(xc2xd)Mxc3x97CS0xc3x97xcex103)2+DSC2]xc2xdxe2x80x83xe2x80x83(1), 
where dx is a virtual crossover diameter, xcex10 is a divergence angle of the beam, and DSC is a divergence component of the beam caused by the repulsive effect of a spatial charge.
Recently, efforts have been made to minimize the spherical aberration coefficient CS0 of the main electronic lens section 605 in order to provide a high precision image by minimizing the spot diameter DS on the face plate 601.
Japanese Laid-Open Publication No. 61-147442, for example, discloses a method for reducing the spherical aberration coefficient CS0 by a built-in division-type resistor. Japanese Laid-Open Publication Nos. 60-208027 and 2-276138, for example, each disclose a method for reducing the spherical aberration coefficient CS0 by forming a convergence electrode of a spiral resistor in the neck of the CRT instead of forming a convergence electrode of the main electronic lens including a plurality of metal cylinders.
The division-type resistor and the spiral resistor are formed in the following manner as described in, for example, Japanese Laid-Open Publication Nos. 61-224402 and 6-275211.
A film is formed of a stable suspension including ruthenium hydroxide (Ru(OH)3) and glass particles and excluding an organic binder. The film is formed on an inner surface of a glass tube (formed of, for example, low melting point lead glass having a softening point of 640xc2x0 C.) by dipping. The film is dried, and then cut into a spiral pattern. Then, the film is baked at a temperature of 400xc2x0 C. to 600xc2x0 C. to form a resistor including ruthenium oxide (RuO2).
Japanese Laid-Open Publication Nos. 61-147442, 55-14627 and 6-275211 disclose another resistor having a high area resistance value, which is formed of RuO2 and high melting point glass particles.
The resistor formed of RuO2 and glass particles is formed in a zigzag pattern on an alumina (e.g., Al2O3) substrate by screen printing. Such a resistor (referred to as a xe2x80x9cglaze resistorxe2x80x9d) has a total resistance value of 300 Mxcexa9 to 1000 Mxcexa9. The alumina used as the substrate has a thermal expansion coefficient of 75xc3x9710xe2x88x927/xc2x0C. and a melting point of 2,050xc2x0 C. Since a CRT requires a resistor which is highly reliable against a high voltage of about 30 kV and an electronic beam, the resistor formed of RuO2 and glass particles is formed by baking at a relatively high temperature of 750xc2x0 C. to 850xc2x0 C.
Japanese Laid-Open Publication No. 7-309282, for example, discloses still another resistor formed of RuO2 and low melting point glass. The low melting point glass is, for example, PbOxe2x80x94B2O3xe2x80x94SiO2xe2x80x94based glass and includes PbO at 65% or more by weight. The softening point of the low melting point glass is about 600xc2x0 C. or less.
The above-described spiral or zigzag-pattern resistors are provided in the neck of the CRT in order to minimize the spot diameter on the fluorescent screen and the deflecting power. In addition, a double anode CRT is also developed in which the electronic lens system includes a high resistance layer in a funnel portion thereof.
A resistor used in the electronic lens system of the CRT provides a potential distribution between the anode electrode and a focus electrode, and thus needs to have a sufficiently high area resistance value of 1 Gxcexa9/xe2x96xa1 to 100 Gxcexa9/xe2x96xa1 (i.e., about 109 xcexa9/xe2x96xa1 to about 1011 xcexa9/xe2x96xa1) in order to prevent a current flow sufficiently to avoid sparking and arc discharge.
Displays utilizing an electron source, such as an FED, also require a high area resistance value provided between an anode and a cathode.
According to the method described in Japanese Laid-Open Publication Nos. 61-224402 and 6-275211, Ru(OH)3, which is an insulating substance, is thermally decomposed while being baked at a temperature of 400xc2x0 C. to 600xc2x0 C. By such thermal decomposition, RuO2, which is a conductive substance, is deposited, and the low melting point glass flows. As a result, fine particles of RuO2 having a diameter of 0.01 to 0.03 xcexcm are deposited around the glass particles, which form a resistor.
Such a method has the following problems in obtaining a high resistance value of 5 Gxcexa9 to 20 Gxcexa9 (area resistance value: 1 Mxcexa9/xe2x96xa1 to 4 Mxcexa9/xe2x96xa1): (i) the dependency of the area resistance value on the baking temperature increases (i.e., the area resistance value significantly changes when the baking temperature slightly changes); (ii) the temperature coefficient of resistance value (TCR) is increased in a negative direction; and (iii) the load characteristic over a long period of time is inferior. The expression xe2x80x9c/xe2x96xa1xe2x80x9d refers to xe2x80x9cper unit areaxe2x80x9d.
The method described in Japanese Laid-Open Publication Nos. 55-14527, 61-147442 and 6-275211 has a problem in that the resultant resistor cannot be formed on an inner surface of the low melting point glass (having a softening point of 640xc2x0 C.) used for the CRT due to the high baking temperature of 750xc2x0 C. to 850xc2x0 C.
According to the method described in Japanese Laid-Open Publication No. 7-309282, the resistor can be formed on an inner surface of the CRT at a low temperature of 440xc2x0 C. to 520xc2x0 C. However, the resistor formed by this method has problems in that (i) the area resistance value significantly changes in accordance with the load characteristic (against application of a voltage of 30 kV at 70xc2x0 C. at 10xe2x88x927 Torr) in the vacuum over a long period of time (5,000 hours); and (ii) the spot diameter on the fluorescent screen is increased due to the load since the TCR is negative.
A tungsten (W)-aluminium oxide-based cermet resistor having a high area resistance value has been developed for use in the electronic tube (see, for example, Japanese Publication for Opposition No. 56-15712). Such a resistor has problems in that (i) a high area resistance value of 109 xcexa9/xe2x96xa1 or more is not obtained; and (ii) the TCR is negative and the absolute value thereof is excessively large.
A resistor having an area resistance value of 1 Gxcexa9/xe2x96xa1 to 100 Gxcexa9/xe2x96xa1 does not need to be shaped into a spiral or zigzag pattern, for use in a CRT. However, the conventional resistive materials have an area resistance value of 1 Mxcexa9/xe2x96xa1 to 100 Mxcexa9/xe2x96xa1. Since such a range of area resistance values is not sufficiently high, the resistor needs to be shaped into a spiral or zigzag pattern.
Attempts have been made to produce an electronic lens system using a high resistance ceramic cylinder without shaping the resistor into a spiral or zigzag pattern (see, for example, Japanese Laid-Open Publication No. 6-275211 and the Proceedings of the 14th International Display Research Conference, pp. 229 to 232 (1994)).
The resistive materials used for this type of electronic lens system include forsterite (2MgOxe2x80xa2SiO2)-based and Al2O3xe2x80x94MnO2xe2x80x94Fe2O3xe2x80x94Nb2O3xe2x80x94based materials. The specific resistance value of these materials is 1011 xcexa9cm (resistance value: 2.4 Gxcexa9 to 240 Gxcexa9). However, it has been pointed out that when the power consumption of a display apparatus, for example, a TV is increased by the negative TCR, the current flowing in the resistive material rapidly increases and possibly thermal runaway occurs.
According to one aspect of the invention, a resistor includes a mixture of at least one of a metal conductive oxide and a transition metal material with an insulating oxide.
In one embodiment of the invention, the resistor is produced using a flame-spraying method.
In one embodiment of the invention, the flame-spraying method includes plasma flame-spraying.
In one embodiment of the invention, the flame-spraying method includes laser flame-spraying.
In one embodiment of the invention, the metal conductive oxide is at least one material selected from the group consisting of titanium oxide, rhenium oxide, iridium oxide, ruthenium oxide, vanadium oxide, rhodium oxide, osmium oxide, lanthanum titanate, SrRuO3, molybdenum oxide, tungsten oxide, and niobium oxide.
In one embodiment of the invention, the metal conductive oxide is at least one material selected from the group consisting of TiO, ReO3, IrO2, RuO2, VO, RhO2, OSO2, LaTiO3, SrRuO3, MoO2, WO2, and NbO.
In one embodiment of the invention, the transition metal material is at least one material selected from the group consisting of titanium, rhenium, vanadium, and niobium.
In one embodiment of the invention, the insulating oxide is at least one material selected from the group consisting of alumina, silicon oxide, zirconium oxide, and magnesium oxide.
In one embodiment of the invention, the insulating oxide is at least one material selected from the group consisting of Al2O3, SiO2, ZrO2, and MgO.
In one embodiment of the invention, the metal conductive oxide is TiO, and the insulating oxide is Al2O3.
In one embodiment of the invention, the resistor has an area resistance value of at least of about 1 Gxcexa9/xe2x96xa1.
According to another aspect of the invention, a cathode ray tube includes the above-described resistor.
According to still another aspect of the invention, a method for producing a resistor includes the steps of forming an electrode on one of an alumina substrate, a glass substrate and a glass tube; and flame-spraying a mixture of at least one of a metal conductive oxide and a transition metal material with an insulating oxide, thereby depositing the mixture on the one of the alumina substrate, the glass substrate and the glass tube.
According to still another aspect of the invention, a field emission display includes an anode, a cathode, and a resistor provided between the anode and the cathode. The resistor includes a mixture of at least one of a metal conductive oxide and a transition metal material with an insulating oxide. The resistor is formed using a flame-spraying method. The resistor has an area resistance value of at least about 1 Gxcexa9/xe2x96xa1.
In one embodiment of the invention, the field emission display further includes a support provided between the anode and the cathode, wherein the support is covered with the resistor.
In one embodiment of the invention, the support includes at least one of glass and alumina.
In one embodiment of the invention, the metal conductive oxide is at least one material selected from the group consisting of titanium oxide, rhenium oxide, iridium oxide, ruthenium oxide, vanadium oxide, rhodium oxide, osmium oxide, lanthanum titanate, SrRuO3, molybdenum oxide, tungsten oxide, and niobium oxide.
In one embodiment of the invention, the metal conductive oxide is at least one material selected from the group consisting of TiO, ReO3, IrO2, RuO2, VO, RhO2, OsO2, LaTiO3, SrRuO3, MoO2, WO2, and NbO.
In one embodiment of the invention, the transition metal material is at least one material selected from the group consisting of titanium, rhenium, vanadium, and niobium.
In one embodiment of the invention, the insulating oxide is at least one material selected from the group consisting of alumina, silicon oxide, zirconium oxide, and magnesium oxide.
In one embodiment of the invention, the insulating oxide is at least one material selected from the group consisting of Al2O3, SiO2, ZrO2, and MgO.
In one embodiment of the invention, the metal conductive oxide is TiO, and the insulating oxide is Al2O3.
According to the present invention, a resistor having a satisfactorily high area resistance value, a satisfactory load characteristic in vacuum, and a positive and stable TCR is obtained without a baking process.
Such a resistor is obtained by flame-spraying a mixture of both or either of a metal conductive oxide or a transition metal material and an insulating oxide toward a substrate using plasma torch or laser. Usable metal conductive oxides include, for example, TiO, ReO3, IrO2, MoO2, WO2, RuO2, and LaTiO2. Usable transition metal materials include, for example, Ti, Re, V and Nb. Usable insulating oxides include, for example, SiO2, Al2O3, ZrO2, and MgO.
Since the particles of the metal conductive oxide or the transition metal material are dispersed among the particles of the insulating oxide, the resistor formed of the above-described mixture has a sufficiently high area resistance value.
The present inventors have found that (i) by using an appropriate metal conductive oxide and/or transition metal material and insulating oxide at an appropriate ratio and an appropriate flame-spraying method, a resistor having a high area resistance value of about 1 Gxcexa9/xe2x96xa1 to about 100 Gxcexa9/xe2x96xa1 is produced; (ii) the resultant resistor has a superior overtime load characteristic to the conventional resistors; and (iii) the TCR of the resultant resistor is small and stable.
Such a resistor does not need to be shaped into a spiral or zigzag pattern and can be easily formed on an alumina substrate of an inner surface of the funnel of a CRT.
Thus, the invention described herein makes possible the advantages of providing (1) a resistor having a satisfactorily high area resistance value produced without baking; (2) a resistor having a satisfactorily high load characteristic over a long period of time in vacuum; (3) a reliable resistor having a small TCR; (4) a method for producing such a resistor; (5) a CRT including such a resistor; and (6) an FED including such a resistor.
These and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.